The present invention relates to a door noise suppressing structure in an open/close body drive apparatus.
Conventionally, for example, Japanese Laid-Open Patent Publication No. 2001-90796 discloses an open/close body drive apparatus. This apparatus uses drive power of a motor to perform opening and closing operation of an open/close body through a regulator fixed to the inner panel in a door.
Noise of the door in which the apparatus according to the above document is used includes noise generated when the motor is activated (motor noise) and noise due to vibration of the inner panel caused by the motor (vibration transmission noise).
In general, the vibration and operating noise of a motor have an order frequency component that is maximized in a high frequency range due to the number of slots and the number of poles of magnets. For example, suppose that the speed of the output shaft of a motor having two poles and eight slots (speed of the rotor after being reduced) is 80 [rpm] (at 12 V, load of 1 N·m), and the speed reduction rate is 79. In this case, the first-order frequency component f1 of the motor is expressed by the following expression.f1=80×79/60=105.3 [Hz]  (1)
The order frequency component fp of the motor at which the order frequency component of the maximum vibration and operating noise exists is a frequency obtained by multiplying the frequency component f1 by the greatest common divisor of the number of poles (2) and the number of slots (8), or 8.fp=105.3×8=842.4 [Hz]  (2)
Since the order frequency component of the maximum vibration and operating noise exists in such a high frequency range, the noise of the door is a high-pitched unpleasant noise.